The general purpose of a chemical vapor deposition (CVD) assembly is to deposit thin films of uniform thickness and chemical composition over a large area substrate such as glass, quartz, sapphire, or iron or titanium sheets.
A variety of reactor systems have been conceived and built, over the years, relating to this field, for example, H. M. Cox, S. G. Hummel and V. G. Keramidas, J. Crystal Growth 79, 900-908 (1986); P. Lee, D. McKenna, D. Kapur and K. F. Jensen, J. Crystal Growth, 77, 120-127 (1986); A. G. Thompson, V. S. Sunderam, G. R. Girard and L. M. Fraas, J Crystal Growth, 94, 901-910 (1989); and mathematically analyzed, A. Sherman, J. Electronic materials, 17, 413-423 (1988); K. F. Jensen, Proc. The Ninth Inter. Conf. on CVD, pp. 3-15, Ed. McD. Robinson, G. W. Cullen, C. H. J. van den Brekel and J. M. Blocher, Jr. Electrochem. Soc., 1984; L. M. Fraas, P. S. McLeod, J. A. Cape and L. D. Partain, J. Crystal Growth, 68, 490-496 (1984).
However, in most cases, uniformity in gas flow has been achieved by either applying a vacuum to the device or rotating the substrate at high speed, or by both means. In one design, H. M. Cox et al, uniform upward flow of gas was achieved by means of a porous frit. The gas impinged on the substrate and at the same time held the substrate in levitation over the frit. But this design was beset by the problems of pressure drop across the frit, difficulty in heating the substrate and the possibility of blocking the frit by solid reaction products due to its proximity to the hot substrate.